Your favorite NES Game?

So, I'm seeing all of these threads for SNES and N64 games, and yet none for the original: the NES. So...what's your favorite NES game? Obscure or mainstream, it really doesn't matter. That game that you just played for hours and (quite possibly) even still go back to play.

Personally, I was always a huge fan of Megaman 5 and the original Legend of Zelda.

I absolutely loved Super Mario Bros! My favorite part was being able to find all of the stars. I just saw on Kickstarter (www.kickstarter.com/.../find-the-secret-stars) that these guys are bringing it to real life through an iPhone app it makes me feel really nostalgic for the old Mario games. Definitely getting this app when it comes out!